Methods for preparation of medical dressing containing antimicrobial agent

ABSTRACT

A medical dressing containing an antimicrobial agent is disclosed. The medical dressing comprises a layered fabric comprising an inner layer of substantially hydrophilic material, an outer layer of substantially hydrophobic material on both sides of the inner layer; and an antimicrobial agent. The antimicrobial agent may be releasably impregnated into the fabric, coated on said fabric or a combination thereof. The antimicrobial agent may be a biguanide, such as polyhexamethylene biguanide (PHMB). The fabric inner layer material may be substantially a cellulose fiber, preferably substantially rayon, and the fabric outer layer material may be substantially polyester, e.g., a combination of textile matrix grade polyester fiber and amorphous binder grade polyester fiber. The fabric is preferably treated with an aqueous solution of surfactant and PHMB to have about 1500-3500 ppm of extractable PHMB.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a medical dressing containing anantimicrobial agent, a sponge formed from such a dressing, and methodsof fabricating such a medical dressing and sponge.

2. Brief Description of Art

Medical dressings have long been used to protect and aid in the healingof wounds. Various forms and constructions of such medical dressings areknown in the art. For instance, U.S. Pat. No. 4,211,227, incorporatedherein by reference, discloses a nonwoven surgical sponge materialcomprising a layered fabric having an inner core or a substantiallyhydrophilic material disposed adjacent at least one outer or surfacelayer, or between a pair of outer layers, of a substantially hydrophobicmaterial. The sponge material is bonded by passing the material throughrolls engraved in a pattern of lands and grooves such that a repeatingpattern of three degrees of compression are imposed on the material.

U.S. Pat. No. 6,369,289, incorporated herein by reference, furtherdiscloses the use of a cellulosic bandage in a method for covering anopen wound by contacting the wound with the bandage having a calculatedamount of antimicrobial agent. The cellulosic bandage may be prepared byproviding at least one rolled beam of cellulosic material onto aperforated drum, inserting the beam of material into an enclosed vessel,adding antimicrobial agent into the vessel, and circulating theantimicrobial agent for a predetermined period of time.

The use of certain kinds of antimicrobial agents is also known in theart. U.S. Pat. No. 4,655,756, for example, relates to a non-wovenmaterial treated with a linear polymeric biguanide having a definedformula, or a mixture of, e.g., polyhexamethylene biguanide (hereafter“PHMB”) dihydrochlorides with defined number average molecular weights.The polymeric biguanide may be present at a concentration of from 500 to5000 ppm and the non-woven. material may be in the form of an articlefor the collection of human body emissions.

Other types of antimicrobial agents are also known. For example, U.S.Pat. No. 5,707,736 discloses a dry, disposable, polymeric product havingsustained-release antimicrobial activity formed from a polymericmaterial having an amine salt antimicrobial agent incorporated therein.The polymeric material may be in the form of fibers, sheets, films, andother stable woven, nonwoven and knitted materials. The antimicrobialagents include, e.g., chlorhexidine gluconate and chlorhexidinehydrochloride.

Additional components , such as adhesives, are also known as componentsof medical dressings. One such surgical dressing is described in U.S.Pat. No. 4,643,180, wherein the dressing comprises a sheet of polymericfilm coated on one side with a water based adhesive of defined thicknesswhich includes an antimicrobial agent deposited on the body facingsurface of the adhesive.

U.S. Pat. No. 4,643,181 also describes a surgical dressing and a processfor making a surgical dressing. The dressing comprises a substratecoated on one surface with a solvent-based skin contact adhesive ofdefined thickness, the adhesive having distributed therein particles ofPHMB. The process involves mixing a defined aqueous solution of PHMBhydrochloride with a solvent which is compatible with the adhesive at amixing speed of no more than 300 rpm, adding the mixture to an adhesive,applying the adhesive to a release surface in an amount of from 40 to 55grams per square meter, drying the adhesive, and applying a substratefor the dressing to the adhesive.

U.S. Pat. No. 4,675,347 relates to an antimicrobial latex compositionand a method of manufacturing a shaped article by repeatedly dipping anarticle into the composition and drying. The composition comprises,e.g., (1) at least one cationic latex component selected from a cationicnatural rubber latex and a cationic synthetic polymer latex and (2) acationic antimicrobial agent incorporated in the cationic latex (1).

U.S. Pat. No. 4,678,704 describes an impregnated fabric materialcomprising a fabric substrate to which has been bonded an activecationic impregnant along with an anionic indicator dye in combinationwith a further cationic component, wherein the dye bonds to the furthercationic component more readily than to the substrate and the furthercationic component competes with the impregnant for bonding to the dye.The cationic impregnant may be a polymeric biguanide, e.g., PHMB.

U.S. Pat. No. 4,837,079 relates to a method for making anantimicrobially active, non-woven web comprising the steps of faintingan unbounded fibrous web, applying throughout the unbonded fibrous weban uncured binder and PHMB hydrochloride as an antimicrobial agent, thePHMB hydrochloride being substantive to the fibers of the web and to thebinder when the web is either wet or dry to prevent the antimicrobialagent from substantially diffusing from the fibers or binder and beingpresent in an amount effective to act as antimicrobial agent, and curingthe binder to bind the fibers together to form an antimicrobiallyactive, non-woven web. An antirnicrobially active, non-woven webcomprising bonded fibers, a binder distributed throughout the fibers inan amount effective to bind the fibers and PHMB hydrochloride which issubstantially prevented from diffusing from the fibers or the binder isalso disclosed. Further disclosed is a wet wiper that is substantiallyidentical to the claimed web, but which additionally contains asubstantially preservative free liquid.

U.S. Pat. No. 5,098,417 relates to a wound dressing for systemicadministration of a physiologically- or biologically-active agent bycontrolled release of the agent into such wound. The wound dressingcomprises a substrate in the form of a fabric or cloth, at least aportion of which is cellulosic, which has been chemically modified toconvert hydroxyl groups in the cellulosic portion to ionic-adsorbingsites, an ionic form of a physiologically- or biologically-active agent(which includes antibacterial agents) adsorbed in the substrate. Theionic bonds hold the agent temporarily to the substrate for controlledrelease therefrom in proportion to the amount of exudate in contact withthe substrate and are formed by adsorbing the agent on the substrate atroom temperature. The ionic bonds are disassociated upon contact withbody exudate from wounds thereby to release the physiologically- orbiologically-active agent in an amount in proportion to the amount ofexudate in contact with the substrate. Chlorhexidine is mentioned as oneof the possible agents.

U.S. Pat. No. 5,141,803 relates to a moistened wipe for cleaning anddelivering a cationic biocide comprising a flexible absorbent nonwovensubstrate impregnated with an aqueous composition comprising definedamounts of potassium sorbate, citric acid, disodiumethylenediaminetetraacetate, a cationic biocide selected from a definedgroup which includes PHMB hydrochloride and the remainder water. The pHof the composition is from about 3.5 to about 4.5.

U.S. Pat. No. 5,156,843 relates to a composition of matter comprising amaterial provided with interstices having solid particles residingtherein. The material is a member selected from the group consisting ofjoined fibers, woven fabric, non-woven fabric, paper, woven cloth,non-woven cloth, foamed plastic and sponge. The solid particles are fromabout one to about 100 microns in diameter and contain a substantiallycontinuous network of pores open to the exterior of the particles, witha functional substance retained in the pores. The functional substancemay be a biocidal substance that can prevent or retard bacterial,microbial, germ or fungal growth.

U.S. Pat. No. 5,498,416 relates to a process for protection ofprostheses, implants and/or catheters, of temporary or permanentimplantable materials against bacterial colonization and infection. Aninfection-resistant device capable of progressively releasing in aqueousmedium an amount of an antibacterial substance fixed to the device, theamount being effective to prevent bacterial contamination of the deviceis disclosed. The device comprises a first coating from a solution inaqueous or organic solvent of a biguanide of a defined general formula(which defines monomeric compounds) and a second coating from a solutionof the antibacterial substance, the second coating overlying the firstcoating, and the first coating ensuring adhesion of the antibacterialsubstance to the device. Illustrative devices are described in theparagraph beginning at column 2, line 60 and include urinary catheters,probes, vascular and intraarterial catheters, cardiacal valvularprostheses, arterial prostheses, cardiac simulators, orthopedicprostheses, ocular or dental implants, shunts that are connecting twosegments of the circulatory system, and suture thread.

U.S. Pat. No. 5,700,742 relates to a method of treating a textilematerial to inhibit microbial growth which comprises applying to thetextile material an oligo- or polymeric biguanide or salt thereof withan inorganic acid or an organic acid having a pK value above 4.5followed by a strong organic acid having a pK value below 4.5 and freefrom any aliphatic or oxyalkylene chain containing 12 or more carbonatoms. A textile material treated in accordance with the claimed methodis also disclosed.

U.S. Pat. No. 5,856,248 relates to cellulose fibers and productscomprising cellulose fibers treated to absorb body secretions whilesubstantially decreasing microbial growth, the fibers being chemicallymodified in a two-stage process comprising a first stage treatment witha water soluble salt of a transition metal and an alkali and a secondstage treatment with a solution of a bisbiguanide compound, therebyforming a bond between the cellulose fibers, the transition metal andthe bisbiguanide compound. The process may utilize a rinsing step toneutral pH between the two aforementioned stages.

U.S. Pat. No. 5,869,073 relates to a liquid composition for applying anon-leachable antimicrobial layer or coating on a surface, comprising asolution, dispersion or suspension of a biguanide polymer, across-linker reacted with the biguanide polymer to form an adduct, andan antimicrobial metal, metal salt (e.g. a silver salt) or metalcomplex, wherein the metal, metal salt or metal complex forms a complexwith the adduct, and wherein the antimicrobial layer or coating does notrelease biocidal levels of leachables into a contacting solution.

U.S. Pat. No. 5,817,325 relates to an article of manufacture havingdisposed on a surface thereof a contact-killing, non-leachingantimicrobial coating which kills microorganisms upon contact. Thecoating comprises an organic polycationic polymer matrix immobilized onthe surface having bound or complexed thereto a surface-accessibleantimicrobial metallic material such that the antimicrobial materialdoes not release biocidal amounts of elutables into the surroundingenvironment. The organic matrix may comprise a biguanide polymer, suchas PHMB or a polymer containing a biguanide moiety.

U.S. Pat. No. 5,849,311 further relates to a contact-killing,non-leaching antimicrobial material, capable of killing microorganismswhich come into contact with the material. The material comprises anorganic polycationic polymer matrix having non-leachably bound orcomplexed thereto an antimicrobial metallic material, such that theantimicrobial material does not release biocidal amounts of elutablesinto the surrounding environment. The polycationic material may be PHMBor a polymer containing a biguanide moiety.

U.S. Pat. No. 5,886,048 relates to a method of treating tumor disease ina human or animal with a therapeutically effective amount of PHMB orsalt thereof.

U.S. Pat. No. 5,985,931 relates to an antimicrobial compositioncomprising defined amounts of PHMB, a quaternary ammonium compound; andparachlorometaxylenol wherein the combination of the three components issaid to exhibit effective antimicrobial activity.

U.S. Pat. No. 5,990,174 relates to a method for improving haze formationand storage stability of an antimicrobial composition consisting ofwater and from 5 to 25% by weight of defined linear polymeric biguanideoligomers. The method comprises adjusting the pH of the aqueousantimicrobial composition to at least 0.1 and less than 5 as determinedusing an indicator thereby improving the resistance to haze formationand storage stability of the aqueous antimicrobial composition whencompared with a corresponding composition at higher pH. Particularconcentration and pH limitations are also disclosed.

U.S. Pat. No. 5,993,840 relates to a composition comprising a non-wovenmaterial containing a mixture of polymeric biguanides subject todesorbtion when the non-woven material is wetted by urine; and ananionic polymer which is substantially insoluble in urine. The anionicpolymer functions to retain the biguanides on the material whencontacted by urine. A process for forming an absorbent layer and amethod of reducing the loss of antimicrobial biguanide, wherein bothinclude the anionic polymer, are disclosed.

European Patent Application No. 136900 discloses the application of PHMBto a surgical drape comprising a non-woven fabric and mentions on page 7that a non-ionic wetting agent in the application formulation isdesirable to provide absorbent characteristics to the fabric.

U.S. Pat. No. 6,017,561 relates to an antibacterial cleaning compositioncomprising a quaternary ammonium compound, an anionic polymer having anacid number greater than 10 wherein the anionic polymer is partially orcompletely neutralized by quaternary ammonium compound to form a polymercomplex and wherein the polymer complex is greater than about 15% byweight of the solids in the composition, a dispersing agent, whichcomprises a surfactant that is selected from the group consisting ofnonionic surfactant, amphoteric surfactant, and mixtures thereof, andoptionally, a solvent. Also disclosed is a sponge device havingantibacterial activity that comprises a sponge; and a polymer complexcomprising a quaternary ammonium compound and an anionic polymer havingan acid number of greater than 10 wherein the anionic polymer ispartially or completely neutralized by the quaternary ammonium compoundto form the polymer complex which is attached to a surface of thesponge. An adsorbent or absorbent matrix which includes the polymercomplex and a method of fabricating an absorbent or adsorbent materialwhich uses at least a quaternary ammonium compound and an anionicpolymer are also disclosed. The ammonium compound may be PHMBhydrochloride. Articles such as sponges are also described.

U.S. Pat. No. 6,160,196 relates to a wound covering comprising ahydrophobic, bacteria-absorbing synthetic or naturally-occurring polymerfiber material, having adhered thereto an antimicrobial active compoundwhich is adapted to not be released into the wound. As described in thespecification and included in certain dependent claims, the material canbe nonwoven and dependent claim 10 recites that the polymer fibermaterial can be selected from a group which includes polyester. Theantimicrobial active compounds are described in the passage that beginsat column 2, line 29 and include chlorhexidine. In this passage, it isstated the compounds “. . . are distinguished by the fact that theyadhere firmly to the wound covering and are not released, or at leastare not released noticeably, into the wound.”

U.S. Pat. No. 6,180,584 relates to a disinfectant composition comprisinga film-forming antimicrobial material (which may be a polymericbiguanide material), an antimicrobial metallic material, and a carrier .The composition, when applied to a surface, forms a non-permanent,adherent, water-insoluble film, wherein the metallic material isnon-leachably bound to or associated with the film. The film does notelute antimicrobial materials into contacting water at levels capable ofimparting disinfecting action to said water, and is removable bytreatment with an alcohol solution. The composition can further includea surfactant.

U.S. Pat. No. 6,235,302 relates to a sponge cloth which is based onregenerated cellulose and has been provided with an internalreinforcement consisting of, e.g., viscose fibers or cotton fibershaving a staple fiber length of 5 to 50 mm. The sponge cloth is obtainedby a process comprising the steps of coagulating and regenerating thecellulose in a bath which has a pH of 13 or higher and which comprisesGlauber's salt, NaOH and water, and impregnating the sponge cloth with abiocidally active agent. Representative agents are described and includeisothiazolone, benzoisothiazolone and benzimidazole derivatives withbiguanides.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a medical dressingcomprising an antimicrobial agent as well as a process of making such amedical dressing. It is a further object to provide a sponge formed fromthe medical dressing as well as a process of making such a sponge.

The medical dressing and sponge formed therefrom are preferablycharacterized by improved antimicrobial behavior. More particularly, ina preferred embodiment, the medical dressing and sponge formed therefromprovide an effective antimicrobial barrier for a wound while alsocontrolling the release of antimicrobial agent contained within an innerportion of the dressing. The antimicrobial agent is preferablyconcentrated within an inner portion absorbent core of the dressingwhile an outer barrier layer portion reduces the release of theantimicrobial agent from the dressing.

It is a further object of the invention to provide a medical dressingand a sponge formed therefrom wherein the outer hydrophobic layer(s)provide(s) non-adherent surfaces to aid in the healing of wounds andwhich reduces or eliminates pain experienced by a patient during changesin the dressing or sponge.

In accordance with one aspect of the present invention, a medicaldressing is provided, comprising:

layered fabric comprising:

-   -   an inner layer of substantially hydrophilic material;    -   an outer layer of substantially hydrophobic material on both        sides of the inner layer; and

an antimicrobial agent, wherein the antimicrobial agent is contained inthe inner layer.

In accordance with another aspect of the invention, the medical dressingof the invention may be in the form of a sponge comprising plies of themedical dressing material.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a cross-sectional view of one form of the medicaldressing containing two outer layers and an inner layer.

FIG. 2 illustrates a surface view of one form of the medical dressingcontaining a cross-shaped incision passing through all plies of thedressing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In one embodiment, the inventive medical dressing is based in part uponthe dressing disclosed in U.S. Pat. No. 4,211,227, the disclosure ofwhich is incorporated herein by reference in its entirety.

In a preferred embodiment, the inventive medical dressing is anantimicrobial drain sponge which is a thermally bonded nonwovenabsorbent material, typically in the form of a square that is 2″×2″ or4″×4″ and having a 6 ply thickness. The material is preferably about 50%polyester and about 50% rayon with each ply formed as a sandwich of alayer of rayon between two layers of polyester. In one embodiment of theinvention, as illustrated in FIG. 1, the outer layers (A and C) may beformed from a hydrophobic material, preferably hydrophobic fibers, suchas polyester fibers. The inner layer (shown as layer B in FIG. 1)comprises a hydrophilic material, preferably hydrophilic fibers, such ascellulosic fibers. More preferably, the cellulosic fibers are rayon.

In order to impart antimicrobial properties, the material that is to becut into the individual sponges is impregnated with an aqueous solutionof an antimicrobial agent, such as polyhexamethylenc biguanide (PHMB).An antimicrobial agent such as PHMB is suitably present in aconcentration of about 0.1 to 0.5% by weight, preferably about 0.15 to0.35% by weight, and most preferably about 0.2 to 0.3% by weight. Asurfactant may also be present in the aqueous solution. For example,commercially available non-ionic surfactants, such as TWEEN® 20, whichis polyoxyethylene (20) sorbitan monolaurate, may be utilized. PHMB usedto prepare the drain sponge may be provided by, e.g., Avecia Inc. underthe designation COSMOCIL® CQ (an aqueous solution of PHMB containing19-21% w/w active ingredient and a pH of 5.0-5.5). The material may beimpregnated with the antimicrobial agent according to any suitabletechnique, such as, e.g., by dip coating the material in a solutioncomprising the antimicrobial agent

The impregnated material may then be pressed at a pressure designed sothat the appropriate level of antimicrobial agent, preferably PHMB,remains in the material. After drying by passing between heated rollers,the material has a residual antimicrobial agent (e.g. PHMB) content offrom 1500 to 3500 ppm. The material is subsequently converted into 4″×4″and 2″×2″, 6 ply drain sponges. The sponges do not include an adhesive,but have a cross-shaped incision in the center (as illustrated in FIG.2) that penetrates all 6 plies so that a drain tube can be passedtherethrough. The antimicrobial agent (e.g. PHMB) can preferably bereleased from the medical dressing or sponge in a moist environment toprovide antimicrobial activity beyond the edges of the sponge for alimited time. In general, the fabric is treated to have about 1500-3500ppm of extractable antimicrobial agent, preferably polyhexamethylenebiguanide.

The antimicrobial agent is preferably releasably impregnated into theinner layer substantially hydrophilic material of the fabric, coated onsaid inner layer or a combination thereof. The antimicrobial agent isalso preferably controllably releaseable from the fabric in an amounteffective as an antimicrobial, more preferably in amount effective as anantimicrobial for a period of up to about 2 days, most preferably up toabout 1 day. The antimicrobial amount is defined as the amount ofantimicrobial agent applied to the dressing that is needed for providingsufficient antimicrobial characteristics, yet without causing irritationof the skin or open wound.

Although the antimicrobial agent may be released from the inner layermaterial of the fabric, the antimicrobial treatment of the fabricprincipally allows the dressing to function as a barrier tocontamination of the wound from sources outside the wound. In addition,due to the absorbent characteristics of the dressing, microbes absorbedwithin the inner layer are prevented from escaping through the dressing.

In general, the antimicrobial agent may be any such agent which suitablyfunctions to provide an antimicrobial property to the inventive medicaldressing. Such antimicrobial agents are described in some of theabove-identified patents, which are herein incorporated by reference forsuch information. Preferred antimicrobial agents include biguanides,especially polyhexamethylene biguanide (“PHMB”).

The fabric inner layer material is substantially hydrophilic, and ispreferably substantially a cellulose fiber, and, more preferably, issubstantially rayon. Other inner layer materials may also be utilized,including polysaccharides, alginates, cotton or carboxy methyl cellulosefiber materials. In general, the inner layer material is “substantiallyhydrophilic” such that wound exudate may be absorbed by the inner layerabsorbent core and that the antimicrobial agent may be contained mostlywithin the absorbent core. In this way, the term “substantiallyhydrophilic” describes the function of the inner layer material. It alsodistinguishes the inner layer material over the function of the“substantially hydrophobic” outer layer material, which provides anantimicrobial barrier property and attenuates or reduces the release ofantimicrobial agent away from the dressing. The improved retention ofantimicrobial agent within the inner layer also lowers the bioburden,i.e., the growth and number of cells, within the dressing during use.

Hydrophobicity and hydrophilicity are commonly reported as thepercentage moisture regain for fibers of the material. For the purposesof the present invention, the terms “substantially hydrophilic” and“substantially hydrophobic”, as they apply to the inner and outer layersrespectively, may be related to the percentage moisture regain forfibers of the respective materials, typically at 70° F. and 65% relativehumidity. The fibers used in the substantially hydrophobic outer layershould have a moisture regain of less than about 10%, preferably lessthan about 5%, and most preferably less than about 2% based on theweight of the dry fiber. The fibers used in the substantiallyhydrophillic inner layer should have a moisture regain of about 5-25,preferably about 10-20, and most preferably about 15-20 times the weightof the dry fiber.

The fabric outer layer material is preferably substantially polyester,and, more preferably, is a combination of textile matrix grade polyesterfiber and amorphous binder grade polyester fiber. The binder fibersfunction to bind, e.g., rayon and textile grade polyester fiberstogether. Suitable inner layer materials include, e.g., Lenzing 8191rayon. Suitable outer layer materials include, e.g. Wellman PolyesterT-203 textile grade polyester and Kosa Polyester 259 amorphous bindergrade polyester. The textile to binder fiber weight ratio is preferablyabout 2:1. Other materials may also be utilized for the outer layer,including, e.g., polyolefins such as polyethylene or polypropylene,nylons, or other thermoplastic fibers.

The hydrophobic layers of the fabric forming the medical dressing mayalso be imparted with a hydrophilic finish. Such a finish may be appliedas a coating of a hydrophilic finishing agent on the outer layers. Itmay also be applied during the impregnation of the inner layer with theantimicrobial agent by including the hydrophilic finishing agent in thesame solution of antimicrobial agent. By contacting the dressingmaterial with the antimicrobial solution containing a hydrophilicfinishing agent, the inner layer is impregnated with the antimicrobialsolution while the outer layers are imparted with a hydrophilic finish.As used herein, the term “hydrophilic finish” is intended to mean thatthe hydrophilic characteristics of the outer layer are increased atleast to some degree by the use of a hydrophilic finishing agent. In apreferred embodiment, the hydrophilic finish helps to improve thefunction of the dressing material or sponge by allowing wound exudate tobe more easily absorbed by the inner layer absorbent core material.Suitable hydrophilic finishing agents include, e.g., surfactants, suchas non-ionic surfactants, which may be typically applied inconcentrations of about 0.1% by weight. As noted above, one suchnon-ionic surfactant is TWEEN® 20, which is polyoxyethylene (20)sorbitan monolaurate, although other such surfactants may also beutilized.

A medical sponge formed from plies of the medical dressing material maycontain several plies of the dressing material, preferably 2-10 plies,more preferably 4-8 plies, and most preferably 6 plies. A cross-shapedincision may be preferably formed in the center of the sponge thatpenetrates all plies, thereby allowing an object to pass through thesponge.

In a preferred aspect, the fabric comprises about 50% by weight rayon,about 33% by weight textile matrix grade polyester, and about 17% byweight binder grade polyester, based on the weight of the fabric.

The fabric of the medical dressing and sponge of the invention may beprocessed to impart softness and improved absorbency, according totechniques known in the art, followed by further processing to form theinventive medical dressing and sponge. Suitable techniques include theuse of microcreping devices such as are commercially available fromMicrex, Corp. for the treatment of nonwoven and other materials. It ispreferred that such treatments provide an absorbency of from about 6-15,preferably 10-15, times the dry weight of the fabric. As used in thecontext of the invention, the term “absorbency” refers to the amount ofliquid material, such as water or wound exudate, that may be absorbed bythe fabric of the medical dressing or sponge.

As compared with other commercial medical dressings and sponges, thepresent invention provides several advantages and benefits. For example,by containing the antimicrobial agent within the inner layer of themedical dressing and the sponge formed therefrom, the release of theantimicrobial agent is controlled such that sensitive wound or skinareas are not adversely irritated. The presence of the antimicrobialagent within the inner layer also allows for the dressing and sponge tofunction effectively as a barrier against contamination of the wound.Contamination of areas outside the wound and dressing or sponge due tothe retention of the wound exudate within the dressing or sponge is alsoreduced or prevented. In addition, the use of the outer hydrophobic(nonwoven) layers provides the dressing and sponge with thecharacteristic of non-adherency to wounds. Further, due in part to thepresence of the outer hydrophobic layer(s), the amount of antimicrobialagent within the inner layer necessary to maintain the antimicrobialeffectiveness of the dressing or sponge is also reduced compared withother commercial products. As such, the present invention provides abenefit of reduced cost associated with the use of lesser amounts ofantimicrobial agent.

The medical dressing of the present invention may also comprise layeredfabric consisting essentially of an inner layer of substantiallyhydrophilic material; an outer layer of substantially hydrophobicmaterial on both sides of the inner layer; and an antimicrobial agent,wherein the antimicrobial agent is contained in the inner layer. As usedin the context of the invention, the phrase “consisting essentially of”is intended to mean that the certain additional components which wouldmaterially affect the basic and novel characteristics of the inventivemedical dressing are not included in the layered fabric. As concerns themedical dressing and sponge of the invention, “consisting essentiallyof” is intended to mean, e.g., that adhesives are not utilized toprepare the layered fabric or that additional agents are not utilized_(t)o bind the antimicrobial agent within the inner layer material ofthe medical dressing.

EXAMPLES

The antimicrobial efficacy of the medical dressing and sponge accordingto the invention has been investigated. Such tests simulate the use ofthe dressing or sponge in practice and are based upon the visualobservation of microbial activity on growth media placed in contact withthe inventive medical dressing or sponge containing a determined amountof microbes. The tests are generally conducted by placing a sample ofthe antimicrobial agent containing dressing or sponge in contact withgrowth medium, adding a small volume of microbe containing aqueoussolution to the medical dressing or sponge, and incubating the testsamples for definite time periods and under controlled temperature andenvironmental conditions. Following the end of the pre-determined timeperiod, the growth medium is visually observed to determine the extent,if any, of microbial activity or growth on the medium. For the purposesof the present invention, an assessment of the antimicrobialeffectiveness of the inventive dressing and sponge against variousmicrobes, including S. aureus, S. epidermidis, E. coli, and P.aeruginosa, has been conducted according to this procedure. In all suchtests, the medical dressing and sponge according to the invention hasbeen determined to be effective to prevent microbial activity on suchgrowth medium. By comparison, control samples not containing anantimicrobial agent, such as PHMB, were determined using the sameprocedures and conditions to not prevent microbial activity on suchgrowth medium.

While the invention has been described in detail by reference tospecific embodiments, the skilled artisan will appreciate that variousmodifications, substitutions, omissions and changes may be made, andequivalents employed, without departing from the spirit of the inventionor the scope of the appended claims.

1-36. (canceled)
 37. A method of preparing a medical dressingcomprising; providing a layered fabric consisting essentially of aninner layer of hydrophilic material, and outer layers of hydrophobicmaterial on both sides of the inner layer, and impregnating a biguanideantimicrobial agent into the inner layer.
 38. The method according toclaim 37 wherein the inner layer of hydrophilic material is rayon, andthe outer layers of hydrophobic material are a combination of textilematrix grade polyester fiber and amorphous binder grade polyester fiber.39. The method according to claim 38, wherein impregnating the biguanideantimicrobial agent comprises contacting the layered fabric with asolution having a surfactant and polyhexamethylene biguanide.
 40. Amethod comprising providing a dressing consisting essentially of aninner layer of hydrophilic material, outer layers of hydrophobicmaterial on both sides of the inner layer, and a biguanide antimicrobialagent, wherein the antimicrobial agent is releasably contained in theinner layer.
 41. The method of claim 40, wherein the biguanideantimicrobial agent is polyhexamethylene biguanide.
 42. The method ofclaim 41, wherein at least one outer layer is a combination of textilematrix grade polyester fiber and amorphous binder grade polyester fiber.43. The method of claim 40, wherein the hydrophilic material is rayon,and the hydrophobic material is a combination of textile matrix gradepolyester fiber and amorphous binder grade polyester fiber.
 44. A methodof preparing a sponge comprising providing layered plies of a substrateconsisting essentially of at least one inner layer of hydrophilicmaterial, outer layers of hydrophobic material on both sides of the atleast one inner layer, and a biguanide antimicrobial agent releasablycontained in the inner layer.
 45. The method of claim 43, wherein thebiguanide antimicrobial agent is polyhexamethylene biguanide.
 46. Themethod of claim 43, further comprising creating a cross-shaped incisionat the center of the layered plies.